Kazumasa Hidaka

Anuran-dependent predation by the giant water bug, Lethocerus deyrollei (Hemiptera: Belostomatidae), in rice fields of Japan

We examined the seasonal dietary patterns of the endangered giant water bug, Lethocerus deyrollei, in rice fields located at Sayo, Hyogo Prefecture, central Japan. The results showed that L. deyrollei underwent a shift in its major food item from breeding adults of Hyla japonica in spring (May and June) to newly metamorphosed juveniles of Rana nigromaculata in summer (July to September). Dietary shifts were shown to correspond with a seasonal fluctuation in the availability of anurans in the rice fields. Although adults of R. nigromaculata were relatively abundant throughout the active season they were infrequently exploited by L. deyrollei, possibly because of the difficulty in handling these large-sized frogs. Therefore, seasonal partitioning of the rice-field habitat by small-sized frogs, adult H. japonica and juvenile R. nigromaculata, would enable L. deyrollei to forage in the rice fields during the extensive active period. From these results, we suggest that the conservation of frog populations is very important for the preservation of this endangered insect and for the maintenance of biodiversity within these rice-field ecosystems.

Notes on paternal care and sibling cannibalism in the giant water bug, Lethocerus deyrolli (Heteroptera: Belostomatidae)

Males of the giant water bug, Lethocerus deyrolli, care for egg masses on vegetation above the water surface. They supply the developing eggs with water and guard them against predators. In the present study, mechanisms by which paternal care is extended were found. Males were found situated just below the water on the natal substrate (usually a stick), and the first instar nymphs were aggregated around the substrate. When disturbed, the males showed aggressive behavior, threatening the intruder with their forelegs. Nymphs up to 12 h old did not attack the offered sibling nymphs or anuran larvae, which are common prey in the field. The 24 h‐old nymphs attacked both prey animals; however, they preferred anuran larvae. Cannibalistic behavior in the nymphs was well developed 72 h after hatching, when the nymphs had already dispersed from the natal substrate. The suppression of sibling cannibalism in younger nymphs would promote the maintenance of tight nymphal aggregations and consequently extend male care in this predatory species.

Community structure and regulatory mechanism of pest populations in rice paddies cultivated under intensive, traditionally organic and lower input organic farming in Japan

ABSTRACT Three different rice production systems in the Chugoku district of southwestern Japan were compared to characterize differences in the arthropod community structures and insect pest regulatory mechanisms. In older traditionally organic rice paddy fields, Nilaparvata lugens was uncommon and was controlled by the sedentary nematode parasite, Agamermis unka. In contrast, in intensively farmed rice paddies, N. lugens was very abundant and A. unka was absent. There were no differences between the intensive paddies and younger traditional paddies. In addition, differences of abundance in spider and collembola populations were not clear in these paddies. In lower-input organic farming systems with no-tillage and winter legume mulch, Sogatella furcifera was much less abundant, and the most important predators, sedentary lycosids, were much more abundant than in the traditionally managed paddy. Densities of N. lugens were similar, but A. unka was not present in the lower-input organic systems. These seden...

Abundance, Diversity, and Seasonal Population Dynamics of Aquatic Coleoptera and Heteroptera in Rice Fields: Effects of Direct Seeding Management

ABSTRACT Recent introduction of modern drainage systems has produced intensely dry conditions in rice farmlands and has degraded habitats for aquatic animals. In this study, we compared water beetle (Coleoptera) and water bug (Heteroptera) communities within rice fields cultivated under different management regimes: V-furrow no-till direct-seeding (DS) and conventional regimes. In DS fields, rice is sown in well-drained fields, and flooding is performed a month later than in conventional rice fields. DS fields are then continuously flooded until harvesting; unlike in conventional fields, where midseason drainage is performed in summer. We observed that DS fields supported higher densities of water beetles and water bugs than conventional fields, probably because of the high compatibility between the flooding period and the reproductive season of the insects. The species richness of water beetles was higher in DS fields than in conventional fields. Overall, DS fields showed higher water beetle and water bug abundance, but the effect was variable for individual species: seven species were more abundant in DS than in conventional fields, whereas two species showed opposite tendencies. Considering the differential responses among species to the management regimes, a mosaic of DS and conventional fields is preferable to either field alone for the conservation of aquatic insects in rice agroecosystems.

Responses of Aquatic Insect, Terrestrial Arthropod, and Plant Biodiversity to the V-Furrow Direct Seeding Management in Rice Fields

The aim of this study was to determine the effects of the V-furrow no-till direct seeding (DS) management on diversity patterns of aquatic insects, terrestrial arthropods and plants in rice paddies. In DS fields, rice is sown in well-drained fields, and flooding is performed 1 month later than that in conventional transplanting rice fields. DS fields are then continuously flooded until harvesting, unlike in conventional fields where a midseason drainage is performed during summer. We observed that diversity patterns of the study organisms were affected by the farming systems. DS fields supported abundant and species-rich assemblages of water beetles and water bugs, presumably because of the high compatibility between the flooding period and the reproductive season of the insects, as well as the absence of seedling box-applied insecticide (clothianidin). The DS farming system positively affected several taxonomic groups (terrestrial arthropods such as Collembola and Araneae, and several endangered plant species), while it negatively affected plant species richness. DS farming enhanced the densities of two rice pest species (Nephotettix cincticeps and Lissorhoptrus oryzophilus). The large differences in the responses of different taxonomic groups to farming systems suggest that a combination of DS and conventional system is preferable to the use of either system alone, for the conservation of aquatic and terrestrial biodiversity in rice agro-ecosystems.